1. Field of the Invention
The present invention relates to a pharmaceutical composition for diabetic complications. More particularly, the invention relates to a therapeutic composition adapted to effectively inhibit progression of diabetic cataract.
Patients who have had diabetes for several years may develop various diabetic complications. The most typical diabetic complications are cataract, retinopathy, nephropathy and neuropathy, and these complications occur at times even while the patients are kept under adequate blood glucose control, leading to blindness due to cataract or retinopathy, progress of nephropathy to renal failure which calls for hemodialysis treatment, peripheral neuroparalysis due to neuropathy or other serious outcomes in some cases. Heretofore, certain amino acid derivatives have been reported to be effective in the treatment of diabetes, arteriosclerosis and cataract or as a liquefying expectorant.
2. Description of the Prior Art
For example, Japanese Patent Laid-Open Application Kokai No. 52-91823 teaches the use of N-(2-mercapto-substituted acyl) amino acid amides as antidiabetic agents or therapeutic agents for artorioslerosis. Japanese Patent Laid-Open Application Kokai No. 52-111572 teaches the use of N-(mercapto-substituted acyl)histidines as therapeutic agents for arteriosclerosis. Japanese Patent Laid-Open Application Kokai No. 55-92315 describes the use of 3-mercaptopropionyl-L-cysteine as a therapeutic agent for cataract. Japanese Patent Laid-Open Application Kokai No. 55-124716 describes the use of methylmethionine sulfonium salts as therapeutic and prophylactic agents for arteriosclerotic heart disease and cerebral diseases. Japanese Patent LaidOpen Application Kokai No. 56-147715 teaches the use of N-acetylcysteine as a therapeutic agent for cataract. Japanese Patent Laid-Open Application Kokai No. 57-209214 teaches the use of cysteine as a therapeutic agent for heavy metal poisoning. Japanese Patent Laid-Open Application Kokai No. 58-88351 describes the use of acylcysteine derivatives as liquefying expectorants and antirheumatic agents. Further, Japanese Patent LaidOpen Application Kokai No. 58-208218 describes the use of a mixture of amino acids such as L-lysine, an amino acid precursor protein, carbohydrates, fats, minerals and vitamins as antidiabetic agents.
However, there is no report on the use of a highly safe protein-constituting amino acid as such in the treatment of diabetic complications, particularly as a therapeutic agent for the treatment of diabetic cataract.
The present inventors early focused attention on cysteine which is a constituent amino acid of glutathione which is known to be essential to the maintenance of crystalline lens transparency and conducted a series of studies on the pharmacologic effects of this amino acid. The studies led to the finding that cysteine has a very remarkable therapeutic effect on diabetic complications and particularly on diabetic cataract. The present invention is predicated on the above finding.
It is, therefore, an object of the present invention to provide a therapeutic composition for diabetic complications. It is another object of the present invention to provide a highly safe and effective pharmaceutical composition for the treatment of diabetic cataract.